systemd/man/sd-json.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="sd-json"
  xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd-json</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd-json</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd-json</refname>
    <refpurpose>APIs for Dealing with JSON Objects</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-json.h&gt;</funcsynopsisinfo>
    </funcsynopsis>

    <cmdsynopsis>
      <command>pkg-config --cflags --libs libsystemd</command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><filename>sd-json.h</filename> is part of
    <citerefentry><refentrytitle>libsystemd</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
    provides APIs to parse, generate, format and otherwise operate with JSON objects.</para>

    <para>The API's central data structure is <type>JsonVariant</type> which encapsulates a JSON object,
    array, string, boolean, number or null value. These data structures are mostly considered immutable after
    construction (i.e. their contents won't change, but some meta-data might, such as reference counters).</para>

    <para>The APIs broadly fall into five categories:</para>

    <itemizedlist>
      <listitem><para>APIs to directly operate with <type>JsonVariant</type> objects, in the
      <function>sd_json_variant*</function> namespace.</para></listitem>

      <listitem><para>APIs to construct complex JSON objects, in the <function>sd_json_build*</function>
      namespace.</para></listitem>

      <listitem><para>APIs to map <type>JsonVariant</type> objects and their fields to matching fields in C
      structures, in the <function>sd_json_dispatch*</function> namespace.</para></listitem>

      <listitem><para>APIs to convert a string representation of a JSON object into a
      <type>JsonVariant</type> object, in the <function>sd_json_parse*</function>
      namespace.</para></listitem>

      <listitem><para>APIs to convert an <type>JsonVariant</type> object into its string representation, in
      the <function>sd_json_format*</function> namespace.</para></listitem>
    </itemizedlist>

    <para>This JSON library will internally encode JSON integer numbers in the range
    <constant>INT64_MIN</constant>…<constant>UINT64_MAX</constant> into native 64bit signed or unsigned
    integers, and will reproduce them without loss of precision. Non-integer numbers are stored in 64bit IEEE
    floating point numbers.</para>

    <para>If the functions return string arrays, these are generally
    <constant>NULL</constant> terminated and need to be freed by the
    caller with the libc
    <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use, including the strings referenced therein.
    Similarly, individual strings returned need to be freed, as
    well.</para>

    <para>As a special exception, instead of an empty string array <constant>NULL</constant> may be returned,
    which should be treated equivalent to an empty string array.</para>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-varlink</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>
</refentry>